Measurement apparatus and a method of using measurement apparatus

ABSTRACT

A method of measurement using a measurement probe system includes the steps of (i) providing a measurement probe system having a measurement probe to a user, the measurement probe system being suitable for use with co-ordinate positioning apparatus and (ii) monitoring usage of the measurement probe system.

This nonprovisional application claims the benefit of U.S. ProvisionalApplication No. 60/996,984, filed Dec. 13, 2007. This application alsoclaims priority from European patent application 07252959.7 filed Jul.26, 2007 and from European patent application 07252965.4 filed Jul. 26,2007. The disclosure of each of the provisional application and of thetwo listed priority European applications is incorporated herein byreference in its entirety.

INTRODUCTION

The present invention relates to measurement apparatus and to methods ofusing such measurement apparatus. In particular, the invention relatesto measurement probes and methods of use thereof.

BACKGROUND OF THE INVENTION

In the field of industrial metrology, it is known to use co-ordinatepositioning apparatus to accurately measure or inspect the dimensions ofan object such as a workpiece. To perform such a measurement function,co-ordinate positioning apparatus moves a measurement probe aroundwithin the working space of the machine so that the positions of variouspoints on the surface of the object to be measured can be determined.

Co-ordinate positioning apparatus includes dedicated co-ordinatemeasuring machines (CMMs) that perform only a workpiece inspectionfunction. Numerically controlled machine tools (e.g. metal cuttingmachines, lathes, machining centres etc) are also one type ofco-ordinate positioning apparatus. For example, a measurement probe maybe loaded into the spindle of a machine tool and used to inspect aworkpiece that has been, or is about to be, machined by that machinetool. Providing a measurement probe system for use with such a machinetool thus offers users the opportunity to automate workpiece set-upand/or perform in-process measurements.

A wide variety of measurement probes are known, including both contactand non-contact devices. Touch trigger probes are one example of ameasurement probe. A touch trigger probe, such as the device describedin U.S. Pat. No. 4,153,998, typically comprises a kinematic mechanism inwhich a stylus holder becomes unseated from an associated seat in theprobe body when the stylus contacts an object. Unseating of thekinematic mechanism also breaks an electrical circuit allowing a“contact” or trigger signal to be generated. As an alternative to suchtouch trigger probes, it is also known to measure stylus deflectionusing strain gauges or the like and to either provide a measure ofstylus deflection or to issue a trigger signal when a certain amount ofstylus deflection has occurred.

It is presently common practice for original equipment manufacturers(OEMs) to offer certain metrology options, such as various measurementprobe systems, when selling machine tool equipment. There are alsovarious companies that produce measurement probe systems that can simplybe added to existing machine tool installations. However, a large amountof research and development activity is required to produce accurate andreliable measurement probe systems and a high level of precision is alsorequired during manufacture to ensure the required measurement accuracyis reliably provided by each device. This leads to the cost ofmeasurement probe systems being, by necessity, not insignificant.

For higher end machine tool apparatus, the cost of fitting a measurementprobe system is small compared to the overall cost of the machine tool.In addition, the financial benefits of increased machine productivitythat are gained by including such a measurement probe system areproportionally high. This is, however, not always the case for lower endmachine tool systems. Typically, for such machine tools, the cost of ameasurement probe option can be a substantial percentage of the cost ofthe machine tool. The high relative cost, possibly combined with amachine tool user that has no awareness of the process improvements thattypically occur when machine tools are fitted with measurement probesystems, has thus lead to lower take-up of metrology options at thelower end of the machine tool market.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, a method of measurementusing a measurement probe system is provided, the method comprising thesteps of; (i) providing a measurement probe system comprising ameasurement probe to a user, the measurement probe system being suitablefor use with co-ordinate positioning apparatus; and (ii) monitoringusage of the measurement probe system.

The present invention has arisen from the recognition that therelatively high upfront cost of providing measurement probe systems,such as measurement probes and associated probe interfaces, is often asubstantial disincentive to potential users who are unaware of thebenefits of incorporating such apparatus into their productionprocesses. Although it is known to provide hire purchase or loanarrangements that allow the purchase cost to be spread over a longerperiod, such arrangements do not reduce the total financial commitmentthat is associated with such purchases but merely reduces the upfrontcost. The method according to the first aspect of the invention thuspermits a manufacturer to sell a measurement probe system at a lowercost than traditionally possible and to recoup the reduction in upfrontincome by charging those users that make ongoing use of the measurementsystem. This recouping of income is achieved through the step ofmonitoring usage of the measurement probe system. The invention thusextends the market for measurement systems to lower end machine toolusers, without the need to reduce the metrology performance of suchsystems. Furthermore, end users also benefit as they are able to assessthe productivity improvements that can be obtained with measurementprobe based systems without having to risk substantial sums of upfrontcapital.

Advantageously, the method also comprises the step of prohibitingfurther usage of the measurement probe system based on the monitoredusage of step (ii). Preferably, the method also comprises the step ofprohibiting usage of the measurement probe system when the monitoredusage exceeds a first predetermined usage threshold. The usage thresholdmay be set at an appropriate level that provides enough usage to set-up,test and/or evaluate the measurement probe system. Alternatively, enoughusage may be provide to allow measurement operations to be performed fora longer period. The amount of usage provided may vary depending on theupfront fee paid by the user.

Conveniently, the method also comprises the step of allowing, on paymentof a refresh fee, further usage of the measurement probe system afterthe first predetermined usage threshold has been exceeded.Advantageously, after payment of the refresh fee, the method comprisesthe further step of prohibiting usage of the measurement probe systemwhen the monitored usage exceeds a second predetermined usage threshold.In other words, a refresh fee may be paid to allow use of themeasurement probe system to be resumed. Resumption may be subject to asecond predetermined usage threshold not being exceeded or may beindefinite. The amount of the refresh fee may be related to the amountof further usage that will be provided. For example, a lower refresh feecould be charged for a small amount of additional usage, whilst a muchhigher fee could be charged to provide continuing, indefinite, usage ofthe system.

The prohibition on further usage of the measurement probe system may beimplemented in various ways. For example, a contractual or othersuitable obligation may be placed on the user not to exceed the agreedlimit. Advantageously, the step of prohibiting further usage of themeasurement probe system comprises the step of preventing the collectionand/or output of measurement data from the measurement probe system. Forexample, the measurement probe system may become inoperable to the userafter the usage limit has been reached.

Instead of pre-paying for certain blocks of measurement probe systemusage, the amount of usage over a period of time could be measured andthe user billed accordingly for such usage. The method may thusconveniently comprise the step of requiring the user to pay a usagecharge based on the monitored usage of step (ii). The charge may bedirectly proportional to the usage, or a banded scale of charges thatvary with usage may be applied.

A variety of measures of measurement probe system usage are possible.Advantageously, step (ii) comprises at least one of counting the numberof measurements acquired by the measurement probe system and measuringthe length of time that the measurement probe system is in use. Thelength of time of use may also be measured in a variety of ways; forexample, the amount of operational time or power-up time may bemeasured.

Preferably, the measurement probe system comprises a probe usage counter(e.g. an electronic counter) for performing step (ii). The measurementprobe system may also include a visual indicator to communicate usageinformation to the user. Alternatively, the co-ordinate positioningapparatus may perform the usage monitoring step (ii).

The method may be implemented using any type of contact or non-contactmeasurement probe. Conveniently, the measurement probe is a touchtrigger probe. The touch trigger probe may be arranged to produce atrigger signal when the stylus is deflected relative to the probe body.When using such a touch trigger probe, step (ii) advantageouslycomprises counting the number of trigger signals produced by themeasurement probe. In such an example, the number of trigger signalstypically relates to the number of points measured using the measurementprobe (ignoring any false triggers etc).

The measurement probe system may include a measurement probe that islinked to a control computer. This control computer may also control, orbe interfaced to, the co-ordinate positioning apparatus. A probeinterface may also be provided as part of the measurement probe systemfor receiving data from the measurement probe and passing that data to acontrol computer. The measurement probe may be hardwired to the probeinterface. Preferably, the measurement probe and the probe interface arein communication via a wireless (e.g. RF or optical) communicationslink. The measurement system may also comprise additional measurementprobes. For example, the measurement system may comprise a spindlemountable measurement probe and a table top (tool setting) measurementprobe. These may pass data to the control computer via a common probeinterface or separate probe interfaces. The overall usage of such ameasurement system may be monitored, or the usage of each measurementprobe may be monitored separately.

The method of the present invention may also comprise the step ofmounting the measurement probe system to any type of co-ordinatepositioning apparatus. A step of using the co-ordinate positioningapparatus to acquire measurements using the measurement probe system mayalso be implemented. Advantageously, step (i) comprises fitting themeasurement probe system to a machine tool. For example, such a step maycomprise loading the measurement probe into the machine tool spindle orplacing the measurement probe in an automated tool changer mechanism sothat it can be automatically loaded into the machine tool spindle as andwhen required. The probe interface may also be physically attached tothe machine tool in a suitable location and electrically interfaced tothe appropriate control computer. The method may also comprise the stepof determining co-ordinate position data using the output of themeasurement probe and the positional (X,Y,Z) information of the machinetool.

According to a second aspect of the invention, a method of measurementusing a measurement probe system comprises the steps of; (i) providing ameasurement probe system comprising a measurement probe to a user, themeasurement probe being suitable for use with co-ordinate positioningapparatus; and (ii) allowing the user to acquire measurements using themeasurement probe system, wherein the acquisition of measurements usingthe measurement probe system is prohibited after a predetermined amountof measurement probe system usage.

The invention, in the second aspect, thus comprises a method ofproviding a measurement probe system to a user and prohibiting use ofthat system after a certain amount of measurement probe usage. Theprohibition may arise from an agreement with the user to cap or restrictusage or, as described in more detail below, the measurement probesystem may be arranged to prevent further usage once the system has beenused for the predetermined amount of measurement probe system usage.This permits lower upfront cost measurement probe systems to be providedto users, with the manufacturer recouping the lost upfront income byrequiring further user payments to extend the usage limit or to replacecomponents of the system.

Advantageously, the acquisition of measurements using the measurementprobe system is prohibited by building a failure mode into themeasurement probe such that the acquisition of measurements is preventedafter a predetermined amount of measurement probe system usage due tofailure of the measurement probe. The failure mode may be a mechanicalfailure mode; e.g. a weakened component that catastrophically failsafter a certain amount of usage. The failure may require all, or some,of the measurement probe system to be replaced. Advantageously, themeasurement probe is formed from a first part and a second part, thefirst part being releasably attachable to the second part to form themeasurement probe, wherein the failure mode is built into the first partof the measurement probe. The first, e.g. disposable, part may thus failafter a certain amount of use thereby preventing further usage of themeasurement probe system. A user may then purchase a replacement firstpart that, when combined with the second part, allows resumption of themeasuring process.

The above described failure mode may also be provided by exhaustion of apower source, such as a battery. For example, the measurement probe maybe supplied with batteries having a certain power storage capacity. Thepower stored in the batteries will be depleted by use of the measurementprobe and, once depleted, the user may be prohibited from further use ofthe measurement probe. For example, the measurement probe may include abattery compartment cover over which a security (e.g. holographic)sticker, seal or tag is placed by the manufacturer. Once the batteriesare expended (i.e. after a certain, predetermined, amount of measurementprobe usage) a refresh fee becomes payable to permit batteryreplacement.

Conveniently, the acquisition of measurements using the measurementprobe system is prevented by powering the measurement probe using anon-replaceable power source (e.g. a battery) such that the acquisitionof measurements is prevented once the power source is exhausted. Themeasurement probe may be provided in first and second parts as describedabove, with the non-replaceable power source being included in the firstpart.

Advantageously, the method comprises the step of measuring usage of themeasurement probe system. In this manner, the prohibition on acquiringfurther measurements using the measurement probe system can be based ona measured usage value. Conveniently, the user is contractuallyinhibited (e.g. by a suitable agreement or contract) from acquiringmeasurements using the measurement probe system after reaching an agreedamount of measurement probe system usage.

The above method is described in terms of users and manufacturers ofmeasurement probe systems. It should, however, be remembered that it isalso common to sell measurement equipment through original equipmentmanufacturers (OEMs) as optional “add-ons” to other equipment. Forexample, measurement probe devices and associated control interfaces areoften offered by machine tool manufacturers as optional items. Themethod is thus in no way limited to the method of sale and alsoencompasses the provision of measuring services through OEMs,distributors, agents etc.

Although the method of the present invention is described in terms ofmeasurement probe systems, it should be noted that the method may beapplied to other types of measuring equipment. Measuring equipment canbe broadly categorised into dimensional and non-dimensional apparatus.Dimensional measurement apparatus allows a physical dimension of anobject to be measured and may include, for example, measurement probes(such as touch trigger or scanning probes), optical position encodersetc. Non-dimensional measurement apparatus is also known for measuring aproperty or characteristic of an object other than a dimension; examplesof such apparatus may include Raman spectrometers and Fourier transforminfrared spectrometers. The method may thus be applied to dimensionaland/or non-dimensional apparatus as required.

Further aspects of the invention relating to apparatus comprising adeactivation portion for inhibiting the use of measurement apparatus aredescribed in Applicant's co-pending European patent application 07252959(agents' ref: 738EP), the disclosure of which is incorporated herein byreference in its entirety. In particular, see pages 1 to 9 thereof.

Further aspects of the invention relating to modular measurement probeapparatus having a stylus module with an in-built failure mode aredescribed in Applicant's co-pending European patent application 07253647(agents' ref: 755EP), the disclosure of which is incorporated herein byreference in its entirety. In particular, see pages 1 to 11 thereof.

In summary, the present invention offers the potential to increase themarket for measurement probe systems without having to compromise on theaccuracy or quality of such systems. From a user's perspective, thelower upfront cost provided by the method reduces the financial riskassociated with the acquisition of measurement probe systems therebymaking such systems a more attractive option.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example only, withreference to the accompanying drawings in which;

FIG. 1 illustrates a measurement probe moved by a machine tool undercomputer control, and

FIG. 2 illustrates a measurement probe having an in-built triggercounter.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring to FIG. 1, a measurement probe 500 is shown mounted to thespindle 502 of a machine tool. The spindle 502 is moveable in threedimensions (X, Y, Z) under the control of a computer controller 504. Themachine tool also comprises, in a known manner, various positionencoders that accurately measure the position (in X,Y,Z) of the spindle502 and pass such position information back to the controller 504.Various alternative types of machine tool are also known.

The measurement probe 500 is a touch trigger probe in which the stylusholder is attached to the probe body by a spring-loaded kinematicarrangement of the type originally described in U.S. Pat. No. 4,153,998,the contents of which are hereby incorporated by reference. In use, aworkpiece contacting stylus 506 is brought into contact with an object510 to be measured. Deflection of the stylus 506 unseats the stylusholder from the probe body thereby breaking an electrical circuit. Aprocessor is provided as part of the measurement probe to analyse theresistance of the circuit and to generate a trigger signal whenever thestylus is deflected by contact with an object; this is described in moredetail in WO03/021182, the contents of which are hereby incorporated byreference.

The measurement probe 500 communicates with a probe interface 508 over aRF wireless link. The wireless link may use a spread spectrum (e.g.frequency hopping) protocol such as, or similar to, that described inmore detail in WO2004/057552, the contents of which are herebyincorporated by reference. Other types of wireless link, for example anoptical link, may alternatively be used. The trigger signal is relayedfrom the probe 500 to the interface 508 via the wireless link and thenpassed to the controller 504. The position of the spindle 502 when thetrigger signal is issued is then stored. This allows, assuming theapparatus has been suitably calibrated, the position of a point on thesurface of the object 510 to be established. Measuring multiple pointsin this manner allows various properties or dimensions of the object tobe determined.

The above described operation of a machine tool based measurement probesystem is known. However, as explained in more detail in the backgroundsection above, end users typically purchase measurement probe systems(e.g. the probe interface 508 and measurement probe 500) with a singleupfront payment. However, the relatively high upfront cost of acquiringsuch a measurement probe system is often a substantial disincentive tomachine tool users who are unaware of the potential benefits ofincorporating such apparatus into their production processes. Inparticular, users of lower end machine tools are often unwilling to takethe risk of investing in a measurement system when they are uncertain ofthe scale of the benefits that will be provided. Although it is known toprovide hire purchase or loan arrangements that allow the purchase costto be spread over a longer period, such arrangements do not reduce thetotal financial commitment that is associated with the purchase (in factinterest charges are likely to increase the total cost) but merelyreduce the amount of upfront expenditure.

In order to increase the uptake of measurement systems, especially forlow end machine tool users, the present inventors have devised a methodfor overcoming the requirement for a large, upfront, financialcommitment. Importantly, this lower cost option does not require anyreduction in the accuracy or reliability of the measurement system. Inaccordance with the present invention, usage of the measurement probesystem is recorded. In the embodiment described with reference to FIG.1, the computer control 504 is arranged to record the number of triggersignals that are received from the measurement system (i.e. from themeasurement probe 500 via the interface 508). This is achieved byrunning an appropriate monitoring program on the computer control 504that stores a count value and causes that count value to increment (ordecrement) each time a trigger signal is received. It should be notedthat the computer control 504 may comprise a numerical controller (NC)interfaced to a separate personal computer or it may comprise a frontend computer that provides numerical control of the machine tool andalso has sufficient processing power to run additional applications.

The measurement apparatus of FIG. 1, and in particular the computercontroller 504, keeps a running total of the number of trigger signalsthat have been issued by the measurement probe. The user may, onpurchasing the equipment, be prohibited from using the measurementsystem after a certain number of trigger signals have been issued. Forexample, purchase of the measurement system may be (e.g. contractually)conditional on it being used to provide no more than a certain number,say ten thousand, trigger signals. This may be considered a first usagethreshold that limits the number of points that can be measured with themeasurement system.

The first usage threshold may be increased before it is exceeded, forexample by purchasing additional “triggers” from the manufacturer ortheir authorised agent etc. If the updated first usage threshold isreached or exceeded, further use of the measurement probe system isprohibited. After use has been prohibited, it may be possible topurchase additional “triggers” or counts that allow use of themeasurement system to be resumed; for example, until a second usagethreshold is reached or exceeded. Third and subsequent usage thresholdsmay subsequently be set in a similar manner. A complete removal of usagerestrictions may also be permitted, for example on payment of a fullrelease or upgrade fee, thereby converting the measurement system into astandard measurement system.

It is important to note that there is no obligation on the user topurchase additional triggers or pay any upgrade fee. This is entirely atthe discretion of the user and can be based on an assessment of thevalue added to the relevant manufacturing process by the measurementsystem. Provision of such a system thus alters the cost/risk balance andmakes the purchase of a measurement system a more attractive option toend users and especially to users of lower end machine tool equipment.The manufacturer also benefits from being able to increase marketpenetration due to the lower upfront cost whilst being able to recoupthe necessary costs from those users who continue to use the measurementsystem once the benefits of the system in the particular applicationhave become apparent.

In the embodiment described with reference to FIG. 1, the computer 504is used to monitor measurement probe usage. However, different methodsof monitoring usage may be implemented. Preferably, such monitoring isperformed in an automated, e.g. electronic, manner but it would bepossible for an operator to manually monitor usage (e.g. by counting orestimating how many times the probe is triggered). In preferredembodiments, the measurement probe system (e.g. the measurement probe orthe probe interface) performs the usage monitoring function.

Referring to FIG. 2, a measurement probe 550 is illustrated thatincludes a trigger counter display 552. The measurement probe 550 is atouch trigger probe of the type describe above but also includes asuitable trigger counter. The trigger counter (not shown) may beprovided as a dedicated trigger counter unit or may be implemented by aprocessor that also performs other probe functions (e.g. deflectionsignal analysis or data communications). The count measured by thetrigger counter is, in this example, made available to the user via atrigger counter display 552, such as a liquid crystal display or thelike, that is provided on the body of the measurement probe.

As shown in FIG. 2, the measurement probe 550 stores a trigger count of“1798” as it is moved towards an object 554. The stylus of themeasurement probe 550 then contacts a point on the surface of the objectthereby deflecting the stylus and generating a trigger signal that ispassed to an associated interface over a wireless link. Generation of atrigger signal in this manner also causes the trigger counter toincrement to “1799” which is displayed to the user. Each time ameasurement point is acquired, the count thus increases by one.

Although a trigger counter display of the type illustrated in FIG. 2provides a convenient way to communicate the trigger count to a user,numerous alternatives are possible. For example, the measurement probemay include an LED that illuminates when a measurement usage thresholdis approached and/or reached. Alternatively, multiple LEDs may beprovided that indicate the number of trigger counts that have beenexpended or are remaining. For example, consider a touch trigger probehaving a usage limit of 10,000 counts. A green LED may be illuminateduntil 8,000 counts have been expended whereupon an amber LED isilluminated. The amber LED is extinguished and a red LED illuminatedwhen the limit is reached. In this manner, some warning that the usagelimit is being approached may be communicated to a user. The triggercount information from the measurement probe may also, or alternatively,be displayed by the probe interface and/or passed to the controlcomputer for display.

It should be noted that although measuring trigger counts provides aconvenient measure of measurement probe usage, other measures could alsoor alternatively be used. For example, the number of parts that havebeen measured by the measurement system could be counted (e.g. by thecomputer controller of the machine tool). As a variant of this, thenumber of parts that have been measured and have been found to be withinacceptable measurement tolerances could be counted, thereby ignoring anymeasurements made on workpieces that have to be scrapped. A time basedusage system may also be implemented. For example, the amount of timethat the measurement system is in use could be measured. This may be ameasure of the duration of machine tool, measurement probe and/or probeinterface activation. Alternatively, it may be possible to measure forhow long the measurement probe has been loaded into spindle and/or movedabout by the machine. The usage of the measurement probe may also bederived from the combination of two or more measures; for example, theusage may be defined by the number of triggers issued and the amount oftime the measurement probe has been active.

The above mentioned prohibition on further use after the usage limit hasbeen reached may rely on the honesty of the user and/or a suitablecontractual requirement can be placed on the user. Alternatively, themeasurement system or the machine tool may include a mechanism (e.g.hardware or software based) that prevents the acquisition or use offurther measurement data after the threshold is reached. A variety ofsuitable embodiments that prevent normal probe operation after a usagelimit has been exceeded are described in more detail below and suchdevices offer the manufacturer the assurance that unauthorised use ofthe measurement system can not occur. Such hardware/software preventionmechanisms may be used in conjunction with contractual requirements.

Instead of setting a usage limit that is not to be exceeded, it is alsopossible to monitor usage of the measurement probe system andperiodically charge the user a usage based fee. This still permits theupfront cost of the measurement probe system to be reduced and allowsusage to be monitored and charged for accordingly. The fee is preferablyset upfront and may include a graduate scale of costs in which eachmeasurement becomes cheaper as more measurements are taken. Once acertain amount of usage has occurred and been paid for, further use ofthe measurement system may not incur any further cost. Again, such ausage based charging system does not require a significant upfrontfinancial commitment from a user and still allows the manufacturer toprofit if the measurement system is found to be advantageous in theuser's particular machining process. This solution therefore also makesmeasurement systems more attractive propositions, especially to users oflower end machine tools.

The above examples that are described with reference to FIGS. 1 and 2relate to touch trigger probes. It should, however, be noted that theinvention is equally applicable to other types of contact and/ornon-contact (e.g. optical, capacitive etc) measurement probes. Forexample, the measurement probe may comprise an analogue or scanningprobe in which data relating to stylus deflection is generated.Similarly, the above examples describe machine tool based systems. Theinvention can also be applied to dedicated co-ordinate measurementmachine (CMMs) or any other type of co-ordinate positioning apparatus.

Embodiments of apparatus comprising a deactivation portion forinhibiting the use of measurement apparatus are described with referenceto FIGS. 1 to 11 in Applicant's co-pending European patent application07252959 (agents' ref: 738EP).

Embodiments of modular measurement probe apparatus having a stylusmodule with an in-built failure mode are described with reference toFIGS. 1 to 3 in Applicant's co-pending European patent application07253647 (agents' ref: 755EP).

1. A method of using a measurement probe system, comprising the stepsof: (i) providing a measurement probe system comprising a measurementprobe to a user, the measurement probe system being suitable for usewith co-ordinate positioning apparatus; and (ii) electronicallymonitoring usage of the measurement probe system.
 2. A method accordingto claim 1 comprising the step of prohibiting further usage of themeasurement probe system based on the monitored usage of step (ii), theprohibiting including disabling the measurement probe.
 3. A methodaccording to claim 2 comprising the step of prohibiting usage of themeasurement probe system when the monitored usage exceeds a firstpredetermined usage threshold.
 4. A method according to claim 3comprising the step of allowing, on payment of a refresh fee, furtherusage of the measurement probe system after the first predeterminedusage threshold has been exceeded.
 5. A method according to claim 4wherein, after payment of the refresh fee, the method comprises thefurther step of prohibiting usage of the measurement probe system whenthe monitored usage exceeds a second predetermined usage threshold, thefurther step of prohibiting including further disabling the measurementprobe.
 6. A method according to claim 2 wherein the disabling comprisesthe step of preventing the output of measurement data from themeasurement probe system.
 7. A method according to claim 1 comprisingcalculating a usage charge based on the monitored usage of step (ii). 8.A method according to claim 1 wherein the electronic monitoringcomprises at least one of counting the number of measurements acquiredby the measurement probe system and measuring the length of time thatthe measurement probe system is in use.
 9. A method according to claim 1wherein the measurement probe system comprises a probe usage counter forperforming step (ii).
 10. A method according to claim 1 wherein themeasurement probe comprises a touch trigger probe comprising a probebody and a stylus, the touch trigger probe being arranged to produce atrigger signal when the stylus is deflected relative to the probe body,wherein the electronic monitoring comprises counting the number oftrigger signals produced by the measurement probe.
 11. A methodaccording to claim 1 wherein the measurement probe system comprises aprobe interface, the measurement probe and the probe interface being incommunication via a wireless communications link.
 12. A method accordingto claim 1 wherein step (i) comprises fitting the measurement probesystem to a machine tool.
 13. A method of using a measurement probesystem, comprising the steps of: (i) providing a measurement probesystem comprising a measurement probe to a user, the measurement probebeing suitable for use with co-ordinate positioning apparatus; (ii)enabling the measurement probe so that the user can acquire measurementsusing the measurement probe system; and disabling the measurement probesystem after a predetermined amount of measurement probe system usage.14. A method according to claim 13 wherein the disabling includesbuilding a failure mode into the measurement probe such that theacquisition of measurements is prevented after a predetermined amount ofmeasurement probe system usage due to failure of the measurement probe.15. A method according to claim 14 wherein the measurement probe isformed from a first part and a second part, the first part beingreleasably attached to the second part to form the measurement probe,wherein the failure mode is built into the first part of the measurementprobe.
 16. A method according to claim 13 wherein the measurement probeincludes a non-replaceable power source and the measurement probe isdisabled once the power source is exhausted.
 17. A method according toclaim 13 comprising the step of electronically measuring usage of themeasurement probe system.